The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the head and neck, such as the ear, nose and throat. The present invention is particularly suited for treating enlarged nasal structures, such as turbinates, polyps or other sinus tissue.
Sinuses are the air-filled cavities insides the facial bones that open into the nasal cavities. Sinusitis is the inflammation of the mucous membranes of one or more of the paranasal sinus cavities. Sinusitis is often associated with a viral or bacterial upper respiratory infection that spreads to the sinuses. When the sinus opening becomes blocked, the cavities fill, producing deep pain and pressure. Postnasal or nasal drainage, nasal congestion with pressure, headaches, sinus infections and nasal polyps are most commonly associated with chronic sinusitis.
Treatment of mild sinusitis typically involves antibiotics, decongestants and analgesics, and is designed to prevent further complications. For more severe or chronic sinusitis, surgery is often necessary to return the nose and sinuses to normal function, particularly with patients who have undergone years of allergy treatment and still suffer from sinus blockage, or patients born with small sinuses and nasal passages. Recent developments in the field of endoscopic surgical techniques and medical devices have provided skilled physicians with instrumentation and methods to perform complicated paranasal sinus surgical procedures. Improved visualization of the nasal cavity and the paranasal sinuses, for example, has now made these anatomical areas more accessible to the endoscopic surgeon. As a result, functional endoscopic sinus surgery (FESS) has become the technique of choice in the surgical approach to sinus disease.
Another nasal symptom, runny noses (e.g., allergic rhinitis or vasomotor rhinitis), is typically caused by small shelf-like structures in the nose called turbinates. Turbinates are responsible for warming and humidifying the air passing through the nose into the lungs. When the air contains an irritant, the turbinates react to the airborne particles by swelling and pouring mucus, as if the body were trying to block and cleanse the breathing passage. Enlarged turbinates cause the air space through the nasal passages to become restricted. In these cases, it would be desirable to reduce the size of the turbinates to alleviate the constriction.
For temporary relief of swollen turbinates, pharmaceutical treatment, such as decongestant nasal sprays and pills, is often prescribed. These measures, however, have limited effectiveness, and the long term use of such nasal sprays typically makes the problem worse. Moreover, pharmaceuticals, particularly decongestant pills may cause high blood pressure, increase the heart rate and, for some people, cause sleeplessness.
Various surgical techniques exist to treat enlarged turbinates, with different instrumentation and degrees of invasiveness. Scalpels, electrocautery and powered instrumentation, such as microdebrider devices and lasers, have been used to reduce the size of body structures, such as swollen tissue, turbinates, polyps and the like. Microdebriders are disposable motorized cutters having a rotating shaft with a serrated distal tip for cutting and resecting tissue. The handle of the microdebrider is typically hollow, and it accommodates a small vacuum, which serves to aspirate debris. In this procedure, the distal tip of the shaft is endoscopically delivered through a nasal passage into the nasal cavity of a patient, and an endoscope is similarly delivered through the same or the opposite nasal passage to view the surgical site. An external motor rotates the shaft and the serrated tip, allowing the tip to cut the polyps or other swollen tissue responsible for the blockage. Once the critical blockage is cleared, aeration and drainage are reestablished and the sinuses heal and return to their normal function.
While microdebriders have been promising, these devices suffer from a number of disadvantages. For one thing, the tissue in the nasal and sinus cavities is extremely vascular, and the microdebrider severs blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon's view of the target site. Controlling this bleeding can be difficult since the vacuuming action tends to promote hemorrhaging from blood vessels disrupted during the procedure. In addition, the microdebrider often must be removed from the nose periodically to cauterize severed blood vessels, which lengthens the procedure. Moreover, the serrated edges and other fine crevices of the microdebrider can easily become clogged with debris, which requires the surgeon to remove and clean the microdebrider during the surgery, further increasing the length of the procedure. More serious concerns, however, are that the microdebrider is not precise, and it is often difficult, during the procedure, to differentiate between the target sinus tissue, and other structures within the nose, such as cartilage, bone or cranial. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone within the nose, and to avoid damaging nerves, such as the optic nerve.
Lasers were initially considered ideal for nasal surgery because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, cartilage, bone and/or cranial nerves often lie within close proximity of the sinus tissue, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.
Recently, RF energy has been used to treat body structures within the nose and throat, such as turbinates. This procedure, which was developed by Somnus Medical Technologies of Sunnyvale, Calif. involves the use of a monopolar electrode that directs RF current into the target tissue to desiccate or destroy portions of the tissue. Of course, such monopolar devices suffer from the disadvantage that the electric current will flow through undefined paths in the patient's body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient's body. In addition, since the defined path through the patient's body has a relatively high impedance (because of the large distance or resistivity of the patient's body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring nerves.
Another disadvantage of conventional RF devices, such as the Somnus monopolar electrode, is that these devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a "cutting effect" along the pathway of localized tissue heating. Thus, the tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site. This collateral tissue damage often causes indiscriminate destruction of turbinate tissue, resulting in the loss of the proper function of the turbinate.